Recently, various golf balls have been proposed that attempt to achieve the intended spin properties and increase the distance of the ball, both by providing the golf ball with a multilayer structure, and also by imparting the core that makes up most of the ball with a specific hardness profile in such a way as to optimize the core hardness profile and the overall hardness and thickness parameters of the ball. Art has also been proposed which, as a means for optimizing the core hardness profile, from the standpoint of the materials and manufacturing method used, provides the core with a two-layer structure and satisfies a desired core hardness profile. Golf balls in which the core is made of two layers are described in, for example, U.S. Pat. Nos. 6,913,547, 7,115,049, 7,267,621, 7,503,855, 7,175,542, 7,367,901, 7,625,302 and 8,702,535.
However, among mid- to high-level amateur golfers and professionals having intermediate to high head speeds, there is a desire for the commercialization of golf balls having a two-layer core that achieve a longer distance and that also, to further increase the enjoyability of the game, maintain the spin performance on approach shots at a high level.